Solid-state NMR spectroscopy will continue to be developed and applied to the study of crystalline and membrane bound peptides. The development of new experimental NMR methods is greatly facilitated by the availability of single and poly-crystalline samples of isotopically labeled peptides synthesized specifically for this purpose. These methods, which have a strong emphasis on structure determination, are applied to 20-30 residue membrane bound helical peptides prepared by solid-phase peptide synthesis or expression in bacteria. The proposed research capitalizes on the rapid progress made in the development of a family of three-and four-dimensional solid-state NMR experiments during the past funding period, and the availability of a new high-field, mid-bore 750 MHz spectrometer dedicated to solid-state NMR spectroscopy. In addition to being able to resolve individual amide resonances in three-dimensional spectra of uniformly 15N labeled peptide samples and to measure the multiple spectral parameters needed for structure determination, these methods can be used to characterize 1H, 13C, and 15N chemical shift tensors in backbone and sidechain sites of polycrystalline samples of peptides. These solid-state NMR methods will be applied to several membrane associated peptides, enabling their stuctures to be determined in membrane bilayers and compared to the structures determined in detergent micelles by solution NMR spectroscopy.